Foam Drainage Research Articles

Hydrodynamics of foams

This brief review article is devoted to all the aspects related to hydrodynamics of foams. For this reason, we focused at first on the methods for studying the basic structural units of the foams—the foam films (FF) and the Plateau borders (PB), thus reviewing the literature about their drainage. After this, we scrutinized in detail the Derjaguin’s works on the electrostatic disjoining pressure along with its Langmuir’s interpretation, the microscopic and macroscopic approaches in the theory of the van der Waals disjoining pressure, the DLVO theory, the steric disjoining pressure of de Gennes, and the more recent works on non-DLVO forces. The basic methods for studying of foam drainage are presented as well. Engineering and other applications of foam are reviewed as well. All these aspects are presented from retrospective and perspective viewpoints.

The foam drainage equation for drainage dynamics in unsaturated porous media

AbstractSimilarity in liquid‐phase configuration and drainage dynamics of wet foam and gravity drainage from unsaturated porous media expands modeling capabilities for capillary flows and supplements the standard Richards equation representation. The governing equation for draining foam (or a soil variant termed the soil foam drainage equation—SFDE) obviates the need for macroscopic unsaturated hydraulic conductivity function by an explicit account of diminishing flow pathway sizes as the medium gradually drains. The study provides new and simple analytical expressions for drainage rates and volumes from unsaturated porous media subjected to different boundary conditions. Two novel analytical solutions for saturation profile evolution were derived and tested in good agreement with a numerical solution of the SFDE. The study and the proposed solutions rectify the original formulation of foam drainage dynamics of Or and Assouline (2013). The new framework broadens the scope of methods available for quantifying unsaturated flow in porous media, where the intrinsic conductivity and geometrical representation of capillary drainage could improve understanding of colloid and pathogen transport. The explicit geometrical interpretation of flow pathways underlying the hydraulic functions used by the Richards equation offers new insights that benefit both approaches.

Foam fractionation for recovering whey soy protein from whey wastewater: Strengthening foam drainage using a novel internal component with superhydrophobic surface

Whey soy proteins (WSP) are acid soluble proteins massively existed in the whey wastewater from the process of soybean protein isolate (SPI) manufacture and they possess high nutritive values and good functional properties. For effectively recovering WSP from the whey wastewater by using foam fractionation, a novel foam column fitted with the cross internal covered by a superhydrophobic coating (SHC) was developed to strengthen foam drainage. The experimental results indicated that SHC could significantly strengthen foam drainage through decreasing the flow resistance of the interstitial liquid in the exterior channels at room temperature. The suitable length of the cross internal with SHC was 600mm and the drainage velocity was dramatically accelerated when it was installed at 50mm from the top of the column. Under the suitable operation conditions, enrichment ratio and recovery percentage of WSP reached 10.5 and 82.3%, respectively. This work provides a new light for strengthening foam drainage at room temperature and facilitates of the industrialization of foam fractionation.

Effects of different hydrocolloids on foaming properties of shrimp puree: a cluster analysis

Using appropriate combination of foaming agents is important to make foams with credible lifetime. This combination can be found through statistical methods. In this study, cluster analysis was employed to study the effect of different type of hydrocolloids, namely xanthan gum (XG), guar, tragacanth, methylcellulose (MC), and Arabic gum (AG) on the properties of shrimp foam to select the best stabilizer. The foam density was significantly increased by increasing concentrations of XG, guar, tragacanth and MC. However, AG had negative effect on the foam density. Shrimp foam without gum addition showed the highest degree of juice separation, so that the rate of foam drainage was decreased by increasing concentrations of all gums. Given the results of cluster analysis, cluster 5 (AG at three concentrations) had the best effect (the lowest drainage volume and foam density) on foaming properties of shrimp puree.

Capillary flows across layers and textural interfaces – Pathways and colloid transport considerations in unsaturated layered porous media

Soils and other geologic porous media often display layering and associated textural contrasts that may alter unsaturated flow and transport pathways. Such natural interfaces are usually represented empirically in continuum flow models with limited mechanistic account of the effect of adjusted pathways across layers on colloid transport and on the nature of unsaturated flow. In this study we present the soil foam drainage equation (SFDE) as alternative framework to simulate unsaturated flow in layered porous media. HypothesisIn contrast to standard continuum flow models, the SFDE explicitly accounts for capillary flow pathways and their adjustment across textural interfaces that in turn define flow geometry for colloidal transport not predicted by continuum models. ExperimentsPore scale water distribution in a layered sand sample was measured using X-ray tomography to quantify capillary flow pathways. Literature values of measured saturation and capillary pressure profiles in layered porous columns were used to evaluate solutions based on the SFDE framework and to deduce velocity profiles and their effects for colloid transport. FindingsThe SFDE framework provides new insights into capillary architecture in unsaturated layered media and opens a new way for using pore scale information (from imaging) to provide the necessary SFDE parameters and potentially improve on the standard continuum representation of capillary flows in layered media.

Synthesis and analysis of foam drainage agent for gas well in Jilin Oilfield

The gas well in Jilin oil field has the characteristics of large temperature variation range and high condensate oil content. So the foam drainage agent of the gas well in Jilin oil field needs to have the performance of oil resistance and less effected by temperature. In this paper, a main foaming agent named lauramidopropyl betaine (LAB) and two kinds of auxiliary foaming agent named sodium alcohol ether sulphate (AES) and lauramidopropylamine oxide (LAO). Through the evaluation of the static foaming capacity and dynamic liquid carrying capacity, the AES is more suitable for LAB. The foaming agent with 70% LAB and 30% AES has 138mm foam height with ROSS-Miles equipment; stirring foam volume can reach 480mL, the half-life of foam is 520s. When the ventilation volume is 8L/min the liquid carrying capacity of 10% of the condensate oil content reached 82g. When the foaming agent concentration is 2%, the liquid carrying capacity of 10% of the condensate oil content reached 75g. When the aeration rate reaches 8-10L/min, the liquid carrying capacity of foam drainage agent can reach the best. The foam drainage agent can retain the performance after 120°C aging for 12h, these performances above can satisfy the requirements for gas well foam drainage in Jilin Oil Field.

The Soil Foam Drainage Equation – an alternative model for unsaturated flow in porous media

The Soil Foam Drainage Equation – an alternative model for unsaturated flow in porous media

New surfactant mixtures for fine foams with slowed drainage

We form and investigate foams stabilized by a triple surfactant mixture containing a nonionic alkyl polyglucoside (APG) in addition to the combination of ionic sodium lauryl-dioxyethylene sulphate (SLES) and zwitterionic cocamidopropyl betaine (CAPB) surfactants. APG improves the surfactants compatibility at alkaline pH. The addition of a readily biodegradable chelating agent methylglycinediacetic acid (MGDA) in the mixture contributes further for the excellent performance even in very hard water.Foam properties are analyzed and compared to those of the single components and to the binary mixture without APG. Foam drainage is successfully controlled by introducing additives suitable for the alkaline conditions: fatty alcohol and/or hydrophobically modified starch.Systematic model experiments are performed to characterize the surface tension and dilatational rheology, and thin films drainage. Slowed foam and thin films drainage is confirmed to correlate with the increased surface visco-elasticity in the presence of fatty alcohols. Temperature impact on the surface properties is used for fine tuning of the foam drainage.

Removal of pyridine from its wastewater by using a novel foam fractionation column

Many of pyridine compounds are considered as typical hazardous refractory organics due to their acute toxic properties and teratogenic effects. Therefore, it is great significant to develop a separation technology with the characters of low energy consumption and environmental compatibility to efficiently remove pyridine from its wastewater. In this work, foam fractionation was used to remove pyridine from its wastewater and a novel foam fractionation column was designed for enhancing interfacial adsorption by vertical sieve tray and strengthening foam drainage by floating tongue type tray, in which bubble diameter was monitored for adjusting feeding flow rate and air flow rate in the continuous foam fractionation process. By comparing the foam properties and the adsorption properties of three anionic surfactants (sodium dodecyl sulfate, sodium alcohol ether sulfate and sodium alpha-olefin sulfonate), sodium dodecyl sulfate was chosen as the optimal collector to remove pyridine at pH 4.5. Under the optimal operating conditions, the enrichment ratio and removal percentage of pyridine could reach as high as 34.5 and 90.2%, simultaneously. Above results indicated that foam fractionation was a practicable technology to efficiently remove a hazardous material from its wastewater by designing an effective foam fractionation column.

Investigation of aqueous foam stability containing pigment colorant using polyoxyethylene nonionic surfactant

To improve foam stability in pigment foaming dispersions, a series of fatty alcohol polyoxyethylene ether (CmEOn) with different alkyl chain and ethylene oxide (EO) chain length (m = 12, 14, 16 and n = 5, 7, 9) were used as foam stabilizer to select the most superior structure for stabilizing foam. The effects of CmEOn on surface tension were investigated which revealed that the CMC of CmEOn in the pigment foaming dispersion decreased with the increase of surfactant hydrophobicity or the decrease of hydrophilicity. Compared to the alkyl chain, EO chain length influenced foam more significantly. C14EO5 in the pigment foaming dispersion showed lowest CMC and equilibrium surface tension. The presence of wormlike micelles and lamellar liquid crystal of SDS and C14EO5 endowed the C14EO5 pigment foaming dispersion with highest viscosity which was distinctly different with other CmEOn. C14EO5 showed the most superior stabilization effects with foam half-life of 172.9 min at 9 wt%. To further analyze the stabilization mechanism of C14EO5, the foam volume and bubble diameter change were observed with a digital microscope. The results demonstrated that the superior stabilization effects of C14EO5 were closely related to its high viscosity, which mainly resulted in the decrease of foam drainage and gas permeability. C14EO5, the optimal CmEOn structure for stabilizing foam, shows excellent foam stabilization capability in pigment foaming dispersions, which is a promising tool to realize pigment foam coloring.

A combined CFD simulation of Plateau borders including films and transitional areas of liquid foams

An integrated computational fluid dynamics model is developed for a combined simulation of Plateau borders, films, and transitional areas between the film and the Plateau borders to reduce the simplifications and shortcomings of available models for foam drainage in micro-scale. Additionally, the counter-flow related to the Marangoni effect in the transitional area is investigated. The results of this combined model show the contribution of the films, the exterior Plateau borders, and Marangoni flow in the drainage process more accurately since the inter-influence of foam’s elements is included in this study. The exterior Plateau borders flow rate can be four times larger than the interior ones. The exterior bubbles can be more prominent in the drainage process in cases where the number of the exterior Plateau borders increases due to the geometry of container. The ratio of the Marangoni counter-flow to the Plateau border flow increases drastically with an increase in the mobility of air-liquid interface. However, the exterior bubbles follow the same trend with much less intensity since typically, the flow is less dependent on the interface of air-liquid in the exterior bubbles. Moreover, the Marangoni counter-flow in a near-wall transition area is less important than an internal one. The influence of air-liquid interface mobility on the average velocity of interior foams is attained with more accuracy with more realistic boundary condition. Then it has been compared with other numerical and analytical results. The contribution of films in the drainage is significant for the mobile foams as the velocity of flow in the film has the same order of magnitude as the velocity in the Plateau border. Nevertheless, for foams with rigid interfaces, film’s contribution in foam drainage is insignificant, particularly for the films near the wall of the container.

Modification and investigation of silica particles as a foam stabilizer

As a solid foam stabilizer, spherical silica particles with diameters ranging from 150 to 190 nm were prepared via an improved Stober method and were subsequently modified using three different silane coupling agents to attain the optimum surface hydrophobicity of the particles. Fourier transform infrared (FTIR) spectra and the measured contact angles were used to characterize the surface properties of the prepared particles. The foam stability was investigated by the foam drainage half-life and the expansion viscoelastic modulus of the liquid film. The results demonstrate that all of the modified silica nanoparticles effectively improve the foam stability. The surface hydrophobicity of the modified particles is found to be a key factor influencing the foam stability. The optimum contact angle of the particles lies in the approximate range from 50° to 55°. The modifier molecular structure used can also influence the stabilizing foam property of the solid particles. The foam system stabilized by (CH3)2SiCl2-modified silica particles exhibits the highest stability; its drainage half-life at maximum increases by 27% compared to that of the blank foam system and is substantially greater than those of the foam systems stabilized by KH570- and KH550-modified particles.

Interplay between bulk self-assembly, interfacial and foaming properties in a catanionic surfactant mixture of varying composition.

The self-aggregation, surface properties and foamability of the catanionic surfactant mixture cetyltrimethylammonium bromide (CTAB)/sodium octyl sulfonate (SOSo) have been investigated to obtain insight on the relation between bulk nanostructures, surfactant packing, and foam stability and aging. Light microscopy, SANS, cryo-TEM, DLS, surface tension, rheometry and direct photography were used to characterize mixtures with varying CTAB molar fraction, xCTAB. In the bulk, self-assembly is richer in the excess CTAB region than in the excess SOSo one. Starting from neat CTAB micelles and on addition of anionic surfactant, there is a change from small ellipsoidal micelles (1 < xCTAB ≤ 0.80) to large rodlike micelles (0.65 ≤ xCTAB ≤ 0.55) and then to vesicles (0 < xCTAB ≤ 0.50), with coexistence regions in between; SOSo-rich mixtures are thus dominated by vesicles. High size polydispersity for the micelles and vesicles is an intrinsic feature of this system. Foam stability is concomitantly impacted by xCTAB. SOSo is a small mobile molecule and so it disrupts foam stability, irrespective of the presence of vesicles. Foams are thus only stable in the CTAB-rich regions, and SANS shows that the shape of micelles and vesicles is unchanged inside the foam. Foam drainage is thereby mostly controlled by the presence of the elongated micelles through the solution viscosity, whereas coarsening is influenced by dense surfactant packing at the gas-liquid interfaces.

Foamed emulsion drainage: flow and trapping of drops.

Foamed emulsions are ubiquitous in our daily life but the ageing of such systems is still poorly understood. In this study we investigate foam drainage and measure the evolution of the gas, liquid and oil volume fractions inside the foam. We evidence three regimes of ageing. During an initial period of fast drainage, both bubbles and drops are very mobile. As the foam stabilises drainage proceeds leading to a gradual decrease of the liquid fraction and slowing down of drainage. Clusters of oil drops are less sheared, their dynamic viscosity increases and drainage slows down even further, until the drops become blocked. At this point the oil fraction starts to increase in the continuous phase. The foam ageing leads to an increase of the capillary pressure until the oil acts as an antifoaming agent and the foam collapses.

Elasticity of particle-loaded liquid foams.

Mixing solid particles with liquid foam is a common process used in industry for manufacturing aerated materials. Desire for improvement of involved industrial processes and optimization of resulting foamed materials stimulates fundamental research on those complex mixtures of grains, bubbles and liquid. In this paper, we generate well-controlled particle-loaded liquid foams and we determine their elastic behavior as a function of particle size (6-3000 μm) and particle volume fraction (0-6%). We focus on both the elastic modulus exhibited by the material at small strain and the strain marking the end of the linear elastic regime. Results reveal the existence of a critical particle-to-bubble size ratio triggering a sharp transition between two well-defined regimes. For small size ratios, the behavior is governed by the mechanical properties of the solid grains, which have been proved to pack in the shape of a foam-embedded granular skeleton. In contrast, bubbles elasticity prevails in the second regime, where isolated large particles contribute only weakly to the rheological behavior of the foamed material. The modeling of elasticity for each regime allows for this transition to be normalized and compared with previously reported particle size-induced effects for foam drainage (Haffner et al. J. Colloid Interface Sci., 2015, 458, 200-208) and solid foam mechanics (Khidas et al., Compos. Sci. Technol., 2015, 119, 62-67). This highlights that rheology and the other properties of particle-loaded foams are subjected to the same size-induced morphological transition.

Evaluation of structural characteristics determining surface and foaming properties of β-lactoglobulin aggregates

Due to its structural versatility and remarkable surface activity, β-lactoglobulin (β-Lg) is a prominent food structuring agent in both its native state and in the form of heat-induced aggregates. In this study, we considered the properties of soluble aggregates of pure β-Lg having a median diameter of 50nm. The behavior of the aggregates at the air/water interface has been probed as a function of pH, with the aim of evaluating the controversial role of surface charge in connection with the functionality of particle-stabilized foams. Based on these new experimental results, it would appear that charge shielding around the isoelectric point (pI) leads to significantly increased foam stability as compared to samples having a significant positive or negative zeta potential. Against expectations, however, maximum foam stability was not linked to minimum foam drainage. High foamability and foam stability have been found to correlate with maxima in the rates of initial surface pressure increase and with interfacial dilatational properties. Evidence for efficient stabilization of the air/water interface was also reflected in a small average bubble size and a low rate of mean bubble area increase for aggregates with pH∼pI. Information from additional comparative experiments on systems with native β-Lg enabled an evaluation of the significance of surface hydrophobicity and aggregate particle size in relation to the foaming properties.

Stable Aqueous Foams from Cellulose Nanocrystals and Methyl Cellulose.

The addition of cellulose nanocrystals (CNC) greatly enhanced the properties of methylcellulose (MC) stabilized aqueous foams. CNC addition decreased air bubble size, initial foam densities and drainage rates. Mixtures of 2 wt % CNC + 0.5 wt % MC gave the lowest density foams. This composition sits near the onset of nematic phase formation and also near the overlap concentration of methylcellulose. More than 94% of the added CNC particles remained in the foam phase, not leaving with the draining water. We propose that the nanoscale CNC particles bind to the larger MC coils both in solution and with MC at the air/water interface, forming weak gels that stabilize air bubbles. Wet CNC-MC foams were sufficiently robust to withstand high temperature (70 °C for 6 h) polymerization of water-soluble monomers giving macroporous CNC composite hydrogels based on acrylamide (AM), 2-hydroxyethyl methacrylate (HEMA), or polyethylene glycol diacrylate (PEGDA). At high temperatures, the MC was present as a fibrillar gel phase reinforced by CNC particles, explaining the very high foam stability. Finally, our CNC-MC foams are based on commercially available forms of CNC and MC, already approved for many applications. This is a "shovel-ready" technology.

Drainage dynamics controlled by corner flow: Application of the foam drainage equation

AbstractIn fast drainage processes water is retained behind the front, defining the plant available water and hydraulic properties of the unsaturated region. In this study we show that the foam drainage equation (FDE) can be applied to predict macroscopic drainage dynamics behind the front because a network of liquid channels controls the liquid flow in both foams and crevices of the pore space. To predict drainage rates at the Darcy scale the FDE is solved numerically after adapting channel geometries and boundary conditions to experimental conditions. The FDE results were in good agreement with measured flow rates behind a drainage front in coarse and fine sand. A notable exception was rapid drainage from fine sand where saturated pore clusters persisted after front passage and drained faster compared to FDE predictions. The dominance of corner capillary flows implied by the good agreement with the FDE formulation could improve the scientific underpinning of the unsaturated hydraulic conductivity function and offers a more realistic view of the geometry of pathways for colloid and pathogen transport in unsaturated media.

The separation of catechol and phenol with each other by two-stage batch foam fractionation

Abstract A great amount of phenolic compounds are considered as carcinogens even at low concentrations and they are highly toxic and widely coexist in effluent discharges. It is a very meaningful work to respectively separate a few trace phenolic compounds from their aqueous solution by foam fractionation. The studies of surface activity and surface excess revealed that catechol had a stronger competitive adsorption on the bubble surface than phenol by using cetyltrimethyl ammonium bromide (CTAB) as a collector. A two-stage batch foam fractionation technology was developed for the respective separation of catechol and phenol from their diluted aqueous solution. In the first stage batch foam fractionation, catechol was effectively separated with a high enrichment ratio of 32.2 and a high removal percentage of 90.25% while the removal percentage of phenol was only 2.32% under the suitable operating conditions. A high selectivity coefficient of catechol over phenol could reach 35.25. Then, phenol existed in the residual solution, which was used as the feeding solution in the second stage. In the second stage batch foam fractionation, the small bubbles were used to enhance the adsorption of phenol. At the same time, the foam fractionation column of an inclined foam phase was used to enhance foam drainage and then phenol was effectively removed with a high enrichment ratio of 44.4 and a high removal percentage of 90.23% under the suitable operating conditions. The results indicated that it was practicable to successfully and respectively separate catechol and phenol from their aqueous solution by using the two-stage batch foam fractionation.

Exact solutions for nonlinear foam drainage equation

In this paper, the modified simple equation method, the exp-function method, the soliton ansatz method, the Riccati equation expansion method and the $$\left( G^{\prime }/G\right)$$ -expansion method are used to construct exact solutions with parameters of the nonlinear foam drainage equation. When these parameters are taken to be special values, the solitary wave solutions and the trigonometric function solutions are derived from the exact solutions. The obtained results confirm that the proposed methods are efficient techniques for analytic treatments of a wide variety of nonlinear partial differential equations in mathematical physics. We compare our results together with each other yielding from these integration tools. Also, our results have been compared with the well-known results of others.